diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
index 266d653b46d..1d279706278 100644
--- a/compiler/rustc_ast_lowering/src/lib.rs
+++ b/compiler/rustc_ast_lowering/src/lib.rs
@@ -497,7 +497,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             self.tcx.hir().def_key(self.local_def_id(node_id)),
         );
 
-        let def_id = self.tcx.create_def(parent, data).def_id;
+        let def_id = self.tcx.create_def(parent, data).def_id();
 
         debug!("create_def: def_id_to_node_id[{:?}] <-> {:?}", def_id, node_id);
         self.resolver.node_id_to_def_id.insert(node_id, def_id);
diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index 60e600f22a2..62c00db2da1 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -1010,12 +1010,19 @@ pub struct FreeRegionInfo {
     pub is_impl_item: bool,
 }
 
+/// This struct should only be created by `create_def`.
 #[derive(Copy, Clone)]
 pub struct TyCtxtFeed<'tcx> {
     pub tcx: TyCtxt<'tcx>,
-    pub def_id: LocalDefId,
-    /// This struct should only be created by `create_def`.
-    _priv: (),
+    // Do not allow direct access, as downstream code must not mutate this field.
+    def_id: LocalDefId,
+}
+
+impl<'tcx> TyCtxtFeed<'tcx> {
+    #[inline(always)]
+    pub fn def_id(&self) -> LocalDefId {
+        self.def_id
+    }
 }
 
 /// The central data structure of the compiler. It stores references
@@ -1507,7 +1514,7 @@ impl<'tcx> TyCtxt<'tcx> {
         // - this write will have happened before these queries are called.
         let def_id = self.definitions.write().create_def(parent, data);
 
-        TyCtxtFeed { tcx: self, def_id, _priv: () }
+        TyCtxtFeed { tcx: self, def_id }
     }
 
     pub fn iter_local_def_id(self) -> impl Iterator<Item = LocalDefId> + 'tcx {
diff --git a/compiler/rustc_middle/src/ty/query.rs b/compiler/rustc_middle/src/ty/query.rs
index ae246c81959..47c1379b308 100644
--- a/compiler/rustc_middle/src/ty/query.rs
+++ b/compiler/rustc_middle/src/ty/query.rs
@@ -334,7 +334,7 @@ macro_rules! define_feedable {
             $($(#[$attr])*
             #[inline(always)]
             pub fn $name(self, value: $V) -> query_stored::$name<'tcx> {
-                let key = self.def_id.into_query_param();
+                let key = self.def_id().into_query_param();
                 opt_remap_env_constness!([$($modifiers)*][key]);
 
                 let tcx = self.tcx;